1. Field of the Invention
The invention relates to the uniform charging and discharging of electrochemical storage cells series-connected, or of groups of several parallel-connected storage cells series-connected to form a battery of the alkali metal and chalcogen type with at least one anode space for the accommodation of the anolyte and one cathode space for the accommodation of the catholyte, both spaces separated from each other by an alkali ion-conducting solid-electrolyte wall.
2. Description of the Prior Art
Such rechargeable electrochemical storage cells with solid electrolytes are very well suited for the construction of storage batteries of higher energy and power density. The .beta.-aluminum oxide electrolyte used in sodium/sulfur storage cells, for instance, allows only sodium ions to pass. This means, in contrast to the lead storage battery, that practically no self-discharge takes place and that no secondary reactions occur when charging such as a water decomposition in the lead/lead-oxide system. Therefore, the current yield, i.e. the Faraday efficiency, of a sodium/sulfur storage cell is near 100%.
These advantages are opposed by the operational disadvantage that such cells must neither be overcharged nor overdischarged, as is possible with lead storage batteries. For this reason, the total capacity in a series-connection is determined by the storage cell having the least capacity. One particularly serious factor is that storage cells used, for instance, in a charged state differing from that of the other storage cells of the battery can never be synchronized with the rest of the line. With the lead storage battery it is possible to bring all storage cells to the same state by overcharging--with hydrogen/oxygen formation (equalizing charge).
To counteract this difference in the charged state of the storage cells of a battery, several storage cells are first connected in parallel before several such groups of parallel-connected storage cells are connected in series. Thereby, due to equalizing currents, the same charging state establishes itself in all storage cells within a group consisting of several parallel-connected storage cells. Viewed statistically, the total capacities of the individual groups differ less from each other than the capacities of individual storage cells.
However, a basic improvement of the charged state of a battery cannot be achieved in this manner, because the parallel block having the smallest capacity continues to determine the total capacity of the battery and the charged states of different blocks cannot be equalized.
Another disadvantage of these electrochemical storage cells shows up when a battery is discharged. For example, if one storage cell of a series-connection of many storage cells or if the parallel-connected storage cells of a group connected in series with other groups is already discharged, the discharge current of the not yet discharged storage cells of the battery acts upon the already discharged storage cells like an extraneously impressed current. Under the effect of this impressed current a polarity reversal of the cell voltage of the discharged storage cells occurs. They continue to discharge and are destroyed in the process.